A preferred method of measuring the water content of various media, including soils, is to insert a waveguide into the medium and measure the propagation time of a voltage impulse or step function through the medium. Details of such methods have been described in U.S. Pat. Nos. 6,657,443 and 6,831,468 which make use of the fact that the propagation time of an electromagnetic wave is proportional to the square root of the permittivity of the medium through which the wave travels.
It is also known that relative permittivity of water is about 80 times that of free space and typically 30 times that of the minerals found in soils. By measuring propagation time, it is then possible to accurately determine the permittivity and also the water content of the medium. Since these measurements are temporal and not based on current and voltage relationships, the resulting water content measurements are free from the effects of the electrical properties of the soil, such as electrical conductivity. There are, however, other soil properties that have an impact on temporal measurements and introduce errors in permittivity and water content measurements.